The present invention relates generally to the field of brush and bristle making, and more specifically, to a bristle sub-assembly having substantially parallel pairs of bristles that are attached to a base string. Bristle sub-assemblies of the type described herein are used in making bristle tufts in a variety of applications, especially toothbrushes.
In my prior co-pending application, there is described a method of forming bristle sub-assemblies which, in brief, involves wrapping a polymeric monofilament around a mandrel and bonding the individual wraps to one or more base strings by applying thermal energy. As seen in FIG. 1, an apparatus 10 for making bristle sub-assemblies includes a rectangularly shaped mandrel 12 having a central passageway and open, opposite axial ends. Four base strings 14, 16, 18 and 20 are fed into one end of the mandrel from respective supply sources 22, 24, 26, and 28.
From the orientation of FIG. 1, the base strings are fed downwardly through the mandrel 12 and pass outwardly from the opposite end. Pulleys or wheels (not shown) are used to turn the base strings substantially 180xc2x0 so that they can run along the respective four corners of the mandrel in the upward direction. While the base strings are running upwardly, a monofilament 30, supplied from a supply 32, is supplied at a controlled feed rate to a wrapping mechanism 34. The wrapping mechanism 34 includes a motor 36 which drives a wrapper 38, through which the monofilament 30 is fed, so that the monofilament is caused to wrap around the mandrel to form a plurality of wraps 40. The wraps are transported upwardly by the upward movement of the base strings.
The wraps pass under heaters 42, one being disposed at each of the four corners of the mandrel 12 (and only two of the four heaters being illustrated in FIG. 1). As the result of application of thermal energy, such as by ultrasonic welding, the monofilament wraps 40 bond to the four base strings, either by melting the base strings or the monofilament, or both. After bonding, the wraps are passed over rotating cutting knives 44, of which there are four in the embodiment of FIG. 1, thereby forming four bristle strings 46, of which only two are partially shown and one is shown being taken up on a spool 48.
FIG. 2 is an enlarged, end view of the bristle string 46, revealing the base string 20 and two bristles 30a and 30b, constituting a bristle pair, which are connected to the base string 20 as a result of the thermoplastic melting of the monofilament 30 during the bonding step. The bristle string 46 would be a continuous length of base string with two, complementary rows of bristles, which as viewed in FIG. 2, would constitute a left row and a right row disposed at complementary angles to each other. Each bristle of one row would be paired, and substantially co-linear with, a bristle from the other row.
The angled orientation of the bristles results from the bonding step involved in the illustrated embodiment. However, variations of the manufacturing process of FIG. 1 could result in a similar bristle string except with all the bristles being co-planar. An example is shown in FIG. 3, in which the bristle pair 30axe2x80x2 and 30bxe2x80x2 of the bristle string 46xe2x80x2 are not only co-linear, but co-planar as well.
While the bristle strings described above are advantageous in making toothbrushes, among other things, by cutting the bristle strings into lengths that become xe2x80x9cbristle sub-assembliesxe2x80x9d that can be used to form bristle tufts on a brush head, the bristle pairs of the bristle sub-assemblies may at times be preferred to be fixed in a parallel orientation with respect to each other, prior to securing the bristle sub-assemblies in a brush.
An object of the present invention is to provide a bristle sub-assembly in which bristle pairs are fixed in an orientation where the bristles of each pair are oriented substantially parallel to each other.
Another object of the present invention is to provide an apparatus for forming bristle sub-assemblies in which the bristles of each bristle pair are fixed in a substantially parallel orientation with respect to each other.
Still another object of the present invention is to provide a method of forming bristle sub-assemblies in which the bristles of each bristle pair are fixed in a substantially parallel orientation with respect to each other.
Yet another object of the present invention is to provide a method of changing the directional orientation of monofilament bristles by heating to a temperature that is high enough to relieve the spring forces that are generated by bending the bristles to the new direction of orientation, yet low enough to avoid causing the molecular structure of the polymeric monofilament bristle material to change significantly. Partial melting at the interface between the bristles and base string is preferred to provide additional bonding between the bristles and base string.
These and other objects are met by providing a bristle sub-assembly which includes a base string, a first row of bristles connected to and extending radially outwardly from the base string, and a second row of bristles connected to and extending radially outwardly from the base string, wherein the first and second rows of bristles are substantially parallel to each other.
In another aspect of the invention, a method of making bristle sub-assemblies includes the steps of forming a bristle string having first and second rows of bristles extending outwardly from a base string, wherein the first and second rows of bristles are disposed in a first orientation with respect to each other, bending the bristles of at least one of the first and second rows of bristles to achieve a second orientation with respect to each other, thereby developing a spring force in the bristles that tends to restore the bristles to the first orientation, heating the bent ones of the bristles to a temperature sufficient to at least relax the spring force while maintaining the bristles in the second orientation and preferably add further bond area between the bristles and base string, and cooling the heated bristles so that the bristles maintain the second orientation.
In another aspect of the present invention, an apparatus for forming bristles sub-assemblies using as a feed material a bristle string having first and second rows of bristles connected to a base string, the first and second rows being in a first orientation relative to each other, wherein the apparatus includes means for bending the bristles of at least one of the first and second rows of bristles to achieve a second orientation of the bristle rows relative to each other, thereby developing a spring force in the bent bristles that biases the bent bristles towards the first orientation, means for heating the bristles bent in the bending step for a time and temperature sufficient to at least relax the spring force and preferably add further bond area between the bristles and base string, and means for cooling the heated bristles so that the bristles maintain the second orientation.